1. [n]  a person who is of equal standing with another in a group
2. [n]  (British) a nobleman (duke or marquis or earl or viscount or baron) who is a member of the British peerage
3. [v]  look searchingly; "We peered into the back of the shop to see whether a salesman was around"

1. \Peer\, v. i. [imp. & p. p. {Peered}; p. pr. & vb. n.
   {Peering}.] [OF. parir, pareir equiv. to F. para[^i]tre to
   appear, L. parere. Cf. {Appear}.]
   1. To come in sight; to appear. [Poetic]
            So honor peereth in the meanest habit. --Shak.
            See how his gorget peers above his gown! --B.
                                                  Jonson.
   2. [Perh. a different word; cf. OE. piren, LG. piren. Cf.
      {Pry} to peep.] To look narrowly or curiously or intently;
      to peep; as, the peering day. --Milton.
            Peering in maps for ports, and piers, and roads.
                                                  --Shak.
            As if through a dungeon grate he peered.
                                                  --Coleridge.
   

2. \Peer\, n. [OE. per, OF. per, F. pair, fr. L. par equal.
   Cf. {Apparel}, {Pair}, {Par}, n., {Umpire}.]
   1. One of the same rank, quality, endowments, character,
      etc.; an equal; a match; a mate.
            In song he never had his peer.        --Dryden.
            Shall they consort only with their peers? --I.
                                                  Taylor.
   2. A comrade; a companion; a fellow; an associate.
            He all his peers in beauty did surpass. --Spenser.
   3. A nobleman; a member of one of the five degrees of the
      British nobility, namely, duke, marquis, earl, viscount,
      baron; as, a peer of the realm.
            A noble peer of mickle trust and power. --Milton.
   {House of Peers}, {The Peers}, the British House of Lords.
      See {Parliament}.
   {Spiritual peers}, the bishops and archibishops, or lords
      spiritual, who sit in the House of Lords.
   

3. \Peer\ v. t.
   To make equal in rank. [R.] --Heylin.
   

4. \Peer\ v. t.
   To be, or to assume to be, equal. [R.]
   

A unit of communications hardware or software that is on the same protocol layer of a network as another. A common way of viewing a communications link is as two protocol stacks, which are actually connected only at the very lowest (physical) layer, but can be regarded as being connected at each higher layer by virtue of the services provided by the lower layers. Peer-to-peer communication refers to these real or virtual connections between corresponding systems in each layer.

To give a simple example, when two people talk to each other, the lowest layer is the physical layer which concerns the sound pressure waves travelling from mouth to ear (so mouths and ears are peers) the next layer might be the speech and hearing centres in the people's brains and the top layer their cerebellums or minds. Although, barring telepathy, nothing passes directly between the two minds, there is a peer-to-peer communication between them.